Air-processed, efficient CH₃NH₃PbI_3−xCl_x perovskite solar cells with organic polymer PTB7 as a hole-transport layer

Abstract

Low-temperature, solution-processed perovskite solar cells (PSCs), which utilized organic poly [4,8-bis[(2-ethylhexyl) [3,4-b]-thiophenediyl] (PTB7) as a hole-transport layer (HTL), achieved a power conversion efficiency (PCE) as high as 13.29% when fabricated in ambient air. Through a comparative study, we demonstrate this PCE value to be superior compared to its counterparts with Spiro-OMeTAD or P3HT as the HTL; the superiority consists in higher fill factor (FF) and open-circuit voltage (V oc ). By probing the absorption spectrum of CH 3 NH 3 PbI 3-x Cl x before and after spin-coating the PTB7, it is discovered that the spin coating of PTB7 has little influence on the quality of the perovskite films. Furthermore, it is shown that PTB7 possesses higher conductivity compared with conventional HTLs, including Spiro-OMeTAD, P3HT and PCDTBT. Moreover, in order to further improve device performance, the prevalent additives lithium bis (trifluoromethylsulphony) imide (LiTFSI) and 4-tert-butylpyridine (t-Bp) are investigated, along with a post-annealing process that is applied to the whole device. The results presented here and the overall fabrication method represent a helpful new approach for fabricating highly efficient perovskite -based photovoltaic devices.

Moisture and Oxygen Enhance Conductivity of LiTFSI‐Doped Spiro‐MeOTAD Hole Transport Layer in Perovskite Solar Cells

“…Improved PCEs also resulted from the addition of Li‐bis(trifluoromethanesulfonyl)‐imide (LiTFSI) dopants to the spiro‐MeOTAD, which substantially enhanced conductivity of the HTL . LiTFSI is a commonly employed dopant for many other HTLs such as Poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA),[1b], poly3hexylthiophene (P3HT), Poly[[(2,4‐dimethylphenyl)imino]‐1,4‐phenylene(6,12‐dihydro‐6,6,12,12‐tetraoctylindeno[1,2‐b]fluorene‐2,8‐diyl)‐1,4‐phenylene] (PIF8‐TAA), and Poly ({4,8‐bis[(2‐ethylhexyl)oxy]benzo [1,2‐ b :4,5‐ b ′]dithiophene‐2,6‐diyl}{3‐fluoro‐2‐[(ethylhexyl‐2)carbonyl]thieno[3,4‐ b ]thiophenediyl}) (PTB7) in perovskite solar cells. The top electrode and the spiro‐MeOTAD HTL beneath are usually the most affected by extrinsic environmental conditions (O 2 , H 2 O, N 2 , temperature, and light) .…”

The Progress of Interface Design in Perovskite‐Based Solar Cells

“…Du et al [ 100 ] employed PTB7 (a p-type materials used in organic photovoltaics (OPV)) as the HTL. Du et al [ 100 ] employed PTB7 (a p-type materials used in organic photovoltaics (OPV)) as the HTL.…”

“…Fullerene modifi cation on TiO 2 was fi rst reported to improve the device performance by facilitating charge extraction at the ETL interfaces. [ 100,171 ] Stability test results suggested that the stability of perovskite was effectively improved under ambient air. [ 170 ] Recently, Yang group [ 109 ] synthesized a triblock fullerene derivative (PCBB-2CN-2C8) to modify the surface of TiO 2 (Figure 16 c,d).…”

Polymer strategies in perovskite solar cells

“…However, a different thiophene‐based donor polymer, PTB7 , demonstrated a remarkably better device efficiency of 13.29% ( J SC of 20.2 mA cm −2 , V OC of 0.94, and FF of 70%) after doping with Li‐TFSI and tBP and device optimization . PTB7 had three‐fold higher conductivity than P3HT (9.5 S/cm against 3.0 S cm −1 for P3HT) and almost five‐fold higher than conventional spiro‐OMeTAD (2.0 S cm −1 ).…”